1. FIELD OF THE INVENTION
The field of the invention is microphones useful in a combination of high wind and high noise environments such as microphones operably attached to helmets worn by motorcycle riders.
2. DESCRIPTION OF THE RELATED ART
In recent years, persons operating in high wind and noise environments, such as motorcycle riders, have enjoyed vast improvements in the ability to carry on conversations. This is especially true in respect to communications between a motorcycle driver and passenger, as well as between a motorcycle driver and/or passenger and other motorcycle drivers and their passengers, all while the motorcycles are moving. Such improvements include the installation of microphones proximate the driver's and passenger's mouth by attachment to the motorcycle helmet, whether by attachment to a boom connected to the lower lip of the side of a motorcycle helmet (one-half or three-quarter style helmet), or within the helmet confines of full coverage style helmets. In addition, the present art also includes the installation of earphones in the helmets of both driver and passenger, e.g., see the Inventors' 1990 patents entitled VENTED MOTORCYCLE HELMET SPEAKER ENCLOSURE (U.S. Pat. No. 4,977,975) and ACOUSTICALLY SHIELDED MOTORCYCLE HELMET SPEAKER ENCLOSURE (U.S. Pat. No. 4,979,586).
As might well be expected, during travel a motorcycle driver and passenger are exposed to vast amounts of noise that is ever present in their immediate environment. In addition to the noise of the motorcycle engine, the road sounds, i.e., sounds of the tires engaging the road, and sounds of nearby vehicles, the motorcycle rider and passenger are also immersed in sounds of air rushing past the motorcycle, past the motorcycle faring, and past the body and face. The noise sounds immediately in front of the mouth of the motorcycle rider wearing a one-half or three-quarter style helmet, or inside a full coverage style motorcycle helmet, present a very special noise environment.
For highest quality sound transmission, the microphone should not, as far as possible, transmit entering sounds except for the driver's and passenger's speech, and as to the speech, it should be as clear as possible. As such, efforts need to be directed to assuring that, as much as possible, only speech sounds enter the microphone immediately in front of the driver's and passenger's respective mouths. If only the party's speech is received by the microphone and converted to electrical signals for transmission to the other rider, or to distant motorcycle drivers and passengers, then much has been contributed to present efficient communication with maximum clarity and minimum distortion.
In today's motorcycle riding, it is common to place a microphone immediately in front of the driver's or passenger's mouth, held there by the helmet being worn. In the case of a one-half or three-quarter style helmet, the microphone housing is supported by a boom attached to the lower lip of the helmet, on one side of the helmet or the other, protruding forward and usually curved around to be situated an inch or so from the operator's mouth. These booms generally consist of flexible spiral steel tubing having a hollow central passageway adapted to conduct the electrical leads from the microphone cartridge to an electronic package mounted on the motorcycle. In most all cases, the microphone is covered with a wind sock made of open cell foam rubber or plastic.
In a full coverage style helmet, a helmet which totally covers the operator's head, the microphone is mounted near the bottom opening (through which one's head passes when putting on the helmet) at a position immediately forward of the operator's mouth.
For both types of helmets, sound entering inlet openings in the microphone housing are situated so as to be in directional alignment with the operator's mouth. Openings on the opposite side of the microphone housing are usually non-existent, primarily because that portion of the microphone housing is usually in a position to receive wind directly when an operator is wearing a helmet with the microphone attached and traveling, especially the one-half and three-quarter style helmet. The noise factor caused by the wind becomes quite severe.
In most instances, the microphone cartridge contained within the housing has a round diaphragm upon which incoming sound waves impinge. The microphone diaphragm reacts by vibrating in resonance with the striking sound waves and as it does, generates perturbations in an electrical signal supplied to the cartridge. These perturbations are conveyed to connected electronic equipment, amplified and distributed to the headsets of other parties, whether by transmission via electrical leads or by radio. The efficiency of the microphone cartridge is at its highest if the sound waves strike the diaphragm as near normal as possible, i.e., transverse to the plane of the annular diaphragm. As a consequence, microphone housings containing the microphone cartridge usually have inlet openings immediately in front of the diaphragm so as to cause sound to strike the diaphragm substantially at right angles.
Since the incoming waves dissipate their energy in making the microphone diaphragm vibrate, it is common to vent the chamber or plenum immediately behind the diaphragm. This is done for various reasons, not the least of which is that failing to vent the plenum behind the diaphragm means that the diaphragm is required to momentarily compress the air behind the diaphragm as the diaphragm moves back and forth during its vibrations. Thus the energy needed to compress the air subtracts from the energy used in moving the diaphragm, making the microphone cartridge less sensitive. In addition, it is common to isolate the plenum immediately behind the diaphragm from the plenum immediately in front of the diaphragm so that sounds impacting upon the front surface of the diaphragm cannot then bounce around to the rear of the housing then engage the backside of the diaphragm. Such will cause distortion in the microphone output signal because the sound waves on the back surface of the diaphragm subtract from the sound waves on the front surface, all tending to reduce the vibration displacement of the diaphragm to incoming sound waves, even those intended to be sensed.
Microphone cartridges generally are button like cylinders having a front flat or slightly cone shaped circular diaphragm which substantially occupies a flat plane even though that plane may have a little thickness. The diaphragm usually has a rear annular ring shaped exposed side. Best results are achieved when the incoming sound waves strike the front side of the diaphragm along the cylindrical axis of the microphone cartridge. This is accomplished easily by situating the front inlet openings in the microphone housing parallel to the cylindrical axis of the cartridge. Similarly, vent holes in the rear side of the microphone housing are opposite the back side of the diaphragm surface, also parallel to the cylindrical axis of the cartridge.
In most situations of motorcycle use, and especially with the one-half and three-quarter style helmet, the microphone housing encapsulating the microphone cartridge has inlet openings in front of the cartridge, but no vent openings at the rear of the housing since such vent openings would be the immediate recipient of wind as the motorcycle rider travels along. This wind, if incoming through vent openings immediately behind the microphone cartridge, would seriously detract from the speech reproduction qualities of the microphone.
In the motorcycle environment, as stated above, the motorcycle driver and passenger are placed in an exceptionally windy and noisy environment, especially due to noise causing elements located immediately below the microphone worn by the operator. These noises, the motorcycle engine noise, road noise, and wind noise, tend to enter the front inlet openings in the microphone housing directly in front of the operator's mouth. Now efforts have been taken to reduce noise input by utilizing front inlet openings which are rather narrow, i.e., the diameter of the opening is quite small compared with the length of the opening through the housing. This tends to make a microphone somewhat directional, i.e., more readily receiving sounds in alignment with the inlet openings rather than sounds coming from other directions, such as below. However, as motorcycle riders can attest, environmental noise does in fact impinge upon the microphone cartridge diaphragm and does substantially contribute to degrading the quality of speech out of the microphone.
As a consequence, if means could be found to effect noise cancelling techniques upon the microphone, the speech reproduction qualities of the microphone would be greatly enhanced. It is to this end that the subject invention is directed.